From 74da0eb39142e4b7e6631dc4f767ec2af86af44b Mon Sep 17 00:00:00 2001
From: Eugen Wissner <belka@caraus.de>
Date: Tue, 10 Sep 2024 11:33:31 +0200
Subject: [PATCH] Consume tokens matching 0 characters at the end

---
 lib/SlackBuilder/LatestVersionCheck.hs       | 109 ++++++++++---------
 tests/SlackBuilder/LatestVersionCheckSpec.hs |   5 +
 2 files changed, 60 insertions(+), 54 deletions(-)

diff --git a/lib/SlackBuilder/LatestVersionCheck.hs b/lib/SlackBuilder/LatestVersionCheck.hs
index d6410dc..a1ed946 100644
--- a/lib/SlackBuilder/LatestVersionCheck.hs
+++ b/lib/SlackBuilder/LatestVersionCheck.hs
@@ -89,72 +89,73 @@ data MatchToken
 -- (v)\\.
 -- @
 match :: Text -> Text -> Maybe Text
-match fullPattern input =
-    case Text.foldl' go (Just startState) input of
-        Just state@MatchState{ pattern' = [] } -> Just $ getField @"matched" state
-        Just state@MatchState{ pattern' = [CloseParenMatchToken] } ->
-            Just $ getField @"matched" state
-        Just state@MatchState{ pattern' = [AsteriskMatchToken] } ->
-            Just $ getField @"matched" state
-        Just state@MatchState{ pattern' = [OneOfMatchToken _] } ->
-            Just $ getField @"matched" state
-        _ -> Nothing
+match fullPattern = go startState
   where
-    digits = toEnum <$> [fromEnum '0' .. fromEnum '9']
-    parsePattern :: Text -> [MatchToken]
-    parsePattern input'
-        | Just (firstChar, remaining) <- Text.uncons input'
-        , firstChar == '\\' =
-            case Text.uncons remaining of
-                Nothing -> []
-                Just ('d', remaining') -> OneOfMatchToken digits
-                    : parsePattern remaining'
-                Just ('.', remaining') -> OneOfMatchToken ('.' : digits)
-                    : parsePattern remaining'
-                Just ('\\', remaining') -> SymbolMatchToken '\\'
-                    : parsePattern remaining'
-                Just (_, remaining') -> parsePattern remaining'
-        | Just (firstChar, remaining) <- Text.uncons input'
-        , firstChar == '['
-        , Just lastBracket <- Text.findIndex (== ']') remaining
-            = OneOfMatchToken (Text.unpack $ Text.take lastBracket remaining)
-            : parsePattern (Text.drop (succ lastBracket) remaining)
-        | Just (firstChar, remaining) <- Text.uncons input' =
-            let token =
-                    case firstChar of
-                        '*' -> AsteriskMatchToken
-                        '(' -> OpenParenMatchToken
-                        ')' -> CloseParenMatchToken
-                        s -> SymbolMatchToken s
-             in token : parsePattern remaining
-        | otherwise = []
     startState = MatchState
         { ignoring = False
         , matched = mempty
         , pattern' = parsePattern fullPattern
         }
-    go :: Maybe MatchState -> Char -> Maybe MatchState
-    go (Just state@MatchState{ pattern' = token : remaining }) nextCharacter =
-        case token of
-            OpenParenMatchToken -> go (Just state{ ignoring = True, pattern' = remaining }) nextCharacter
-            CloseParenMatchToken -> go (Just state{ ignoring = False, pattern' = remaining }) nextCharacter
-            AsteriskMatchToken -> Just $ matchSymbolToken state nextCharacter
-            SymbolMatchToken patternCharacter
-                | patternCharacter == nextCharacter -> Just
-                    $ matchSymbolToken state{ pattern' = remaining } nextCharacter
-                | otherwise -> Nothing
-            OneOfMatchToken chars
-                | nextCharacter `elem` chars ->
-                    Just $ matchSymbolToken state nextCharacter
-                | otherwise ->
-                    go (Just state{ pattern' = remaining }) nextCharacter
-    go _ _ = Nothing
+    go :: MatchState -> Text -> Maybe Text
+    -- There is no input, look at the remaining tokens.
+    go MatchState{ pattern' = [], matched } "" = Just matched
+    go state@MatchState{ pattern' = OpenParenMatchToken : tokens } input' =
+        go (state{ ignoring = True, pattern' = tokens }) input'
+    go state@MatchState{ pattern' = CloseParenMatchToken : tokens } input' =
+        go (state{ ignoring = False, pattern' = tokens }) input'
+    go state@MatchState{ pattern' = AsteriskMatchToken : tokens } input'
+        | Just (nextCharacter, leftOver) <- Text.uncons input' =
+            go (matchSymbolToken state nextCharacter) leftOver
+        | otherwise = go state{ pattern' = tokens } ""
+    go state@MatchState{ pattern' = OneOfMatchToken chars : tokens } input'
+        | Just (nextCharacter, leftOver) <- Text.uncons input'
+        , nextCharacter `elem` chars =
+            go (matchSymbolToken state nextCharacter) leftOver
+        | otherwise =
+            go (state{ pattern' = tokens }) input'
+    go state@MatchState{ pattern' = SymbolMatchToken patternCharacter : tokens } input'
+        | Just (nextCharacter, leftOver) <- Text.uncons input'
+        , patternCharacter == nextCharacter =
+            go (matchSymbolToken state{ pattern' = tokens } nextCharacter) leftOver
+        | otherwise = Nothing
+    -- All tokens are processed, but there is still some input left.
+    go MatchState{ pattern' = [] } _ = Nothing
     matchSymbolToken state nextCharacter
         | getField @"ignoring" state = state
         | otherwise = state
             { matched = Text.snoc (getField @"matched" state) nextCharacter
             }
 
+parsePattern :: Text -> [MatchToken]
+parsePattern input'
+    | Just (firstChar, remaining) <- Text.uncons input'
+    , firstChar == '\\' =
+        case Text.uncons remaining of
+            Nothing -> []
+            Just ('d', remaining') -> OneOfMatchToken digits
+                : parsePattern remaining'
+            Just ('.', remaining') -> OneOfMatchToken ('.' : digits)
+                : parsePattern remaining'
+            Just ('\\', remaining') -> SymbolMatchToken '\\'
+                : parsePattern remaining'
+            Just (_, remaining') -> parsePattern remaining'
+    | Just (firstChar, remaining) <- Text.uncons input'
+    , firstChar == '['
+    , Just lastBracket <- Text.findIndex (== ']') remaining
+        = OneOfMatchToken (Text.unpack $ Text.take lastBracket remaining)
+        : parsePattern (Text.drop (succ lastBracket) remaining)
+    | Just (firstChar, remaining) <- Text.uncons input' =
+        let token =
+                case firstChar of
+                    '*' -> AsteriskMatchToken
+                    '(' -> OpenParenMatchToken
+                    ')' -> CloseParenMatchToken
+                    s -> SymbolMatchToken s
+            in token : parsePattern remaining
+    | otherwise = []
+  where
+    digits = toEnum <$> [fromEnum '0' .. fromEnum '9']
+
 -- * Packagist
 
 newtype PackagistPackage = PackagistPackage
diff --git a/tests/SlackBuilder/LatestVersionCheckSpec.hs b/tests/SlackBuilder/LatestVersionCheckSpec.hs
index bc4a0f2..cfdd195 100644
--- a/tests/SlackBuilder/LatestVersionCheckSpec.hs
+++ b/tests/SlackBuilder/LatestVersionCheckSpec.hs
@@ -41,3 +41,8 @@ spec = do
             let expected = Nothing
                 actual = match "2.6.0-rc1" "2.6.0"
              in actual `shouldBe` expected
+
+        it "consumes the last token matching nothing" $
+            let expected = Just "abc"
+                actual = match "abc\\d\\d" "abc"
+             in actual `shouldBe` expected